The present invention relates to engine systems, and more particularly to engine systems for aircraft capable of both helicopter-type flight and fixed-wing flight.
Aircraft are known that enable both helicopter-type flight and fixed-wing flight. One example of such an aircraft is described in U.S. Pat. No. 5,454,530. The single-engine X-50 “Dragonfly” aircraft from The Boeing Company, Chicago, Ill., is similar to that described in U.S. Pat. No. 5,454,530. These aircraft are commonly referred to as canard rotor wing (CRW) vehicles.
CRW vehicles include a canard assembly and a reaction rotor. The reaction rotor is driven (i.e., rotated) for relatively low speed helicopter-type flight, which enables maneuvers such as vertical takeoffs and landings. The reaction rotor can be locked in place for higher speed wing-born (fixed-wing) flight, which enables substantially horizontal flight. The canard assembly provides lift that is critical during changeover between helicopter-type flight and fixed-wing flight, and vice-versa.
However, there are numerous challenges with existing designs. For instance, single-engine designs have limitations with regard to engine placement, maintenance accessibility, etc. Moreover, safety risks are associated with single engine designs, because an engine shutdown event generally has greater safety risks over aircraft having a second engine that can remain operational for partial or emergency flight.
Known twin-engine designs route engine exhaust flows through common (i.e., coupled) ducting, which presents operational problems. For instance, acoustic coupling of exhaust flows from the engines, which may arise from exhaust flow characteristics and/or minor irregularities (i.e., differences) between adjacent engines, can be communicated through common manifold ducting. Moreover, sudden-onset stall or surge events in one event cannot be adequately compensated for, and can have an undesirable adverse impact on the adjacent engine coupled through common ducting.